Nernst effect in the phase-fluctuating superconductor InO$_x$

TL;DR

This study investigates the Nernst effect in amorphous InO$_x$, revealing continuous evolution through the superconducting transition due to phase fluctuations, contrasting with conventional BCS behavior and highlighting the role of phase coherence.

Contribution

It provides new insights into phase fluctuations in low-density superconductors, showing a continuous Nernst signal across T_c unlike traditional superconductors.

Findings

Nernst signal evolves smoothly through T_c in InO$_x$

Ghost critical field indicates non-diverging correlation length

Phase fluctuations persist below T_c

Abstract

We present a study of the Nernst effect in amorphous 2D superconductor InO$_x$, whose low carrier density implies low phase rigidity and strong superconducting phase fluctuations. Instead of presenting the abrupt jump expected at a BCS transition, the Nernst signal evolves continuously through the superconducting transition as previously observed in underdoped cuprates. This contrasts with the case of Nb$_{0.15}$Si$_{0.85}$, where the Nernst signal due to vortices below T$_{c}$ and by Gaussian fluctuations above are clearly distinct. The behavior of the ghost critical field in InO$_x$ points to a correlation length which does not diverge at $T_c$, a temperature below which the amplitude fluctuations freeze, but phase fluctuations survive.